1. Field of the Invention
The present invention relates to a chain guide for a motorcycle, which is useful for preventing a drive chain from coming off a sprocket on the motorcycle's rear wheel due to a swinging motion of a rear swing arm.
2. Description of the Background Art
Certain chain guides for motorcycle drive chains have been known. For example, a chain guide has been provided at the rear portion of the a motorcycle's rear swing arm, for preventing a chain from coming off a sprocket due to vibrations of the rear swing arm or the like under harsh traveling conditions. There is an increased risk of the chain coming off the sprocket where the vertical amplitude of vibrations of the rear swing arm becomes significantly large.
However, during travel, the known chain guide is adapted to be contacted by the moving chain at the position of installation thereof. Therefore, abrasion of the chain guide is a problem with the known designs.
A chain guide which is formed of plastic resin, with an attached guide holder to increase the strength and the rigidity thereof, is proposed in Japanese published Patent Document JP-UM-B-5-20637.
FIGS. 7 and 8 of the drawings in the present document are reproductions of FIG. 4 and FIG. 2, respectively, from Japanese published Patent Document JP-UM-B-5-20637. However, components of FIGS. 7 and 8 hereof have been renumbered from the original, and the names of the components are partly changed.
In the prior art chain guide 100 from Japanese published Patent Document JP-UM-B-5-20637, as illustrated in FIGS. 7-8, the chain guide 100 includes a guide holder 101 formed of a metal such as aluminum, and having a substantially U-shape in cross-section. The chain guide 100 also includes a chain guide member 102 formed of plastic resin or the like for fitting inside of the guide holder 101. The chain guide 100 is attached to the lower rear surface 107 of the rear swing arm 106 via a mounting stay 108.
During operation of the motorcycle, the chain 109 is adapted to be contacted by the moving chain guide member 102. When these components come into contact many times, abrasion of the chain guide member 102 results. At a chain-introducing portion 105 of the chain guide 100, the chain guide member 102 is subjected to a large amount of abrasion.
Once the chain guide member has become abraded, since the chain guide member 102 and the guide holder 101 are oriented flush with each other on the side surface of the introducing portion, the chain 109 may come into contact with the guide holder 101, in association with a swinging motion of the rear swing arm 106. When durability is considered, it would be best to avoid interaction between the guide holder 101 and the chain 109, since these components are both formed of metal. When it is found that these metal components come into contact after a certain amount of usage, replacement of the device with a larger chain guide, or increased costs are likely.
Also, when the guide holder 101 becomes s deformed or scarred due to contact or the like between the guide holder and the chain, it takes time for replacement thereof, and during this time, the vehicle becomes temporarily unusable. In the case of off-road motorcycle racing, for example, it may affect the result of the race. Therefore, easy assembly and disassembly of the guide holder are desired.
Although the known motorcycle chain guides are useful for their intended purposes, there is still a need for an improved chain guide, designed to minimize contact between a guide holder and a motorcycle chain during use. It would be advantageous if such a chain guide were easy to maintain and service.